Degradation of pesticides by Phanerochaete chrysosporium in solid substrate fermentation

The use of the lignin degrading system of the white rot fungus Phanerochaete chrysosporium in solid substrate fermentation (SSF) for degradation of pesticides was investigated. The studies were made in laboratory scale and by using a 1.5 m3-bioreactor with autoclaved and non-autoclaved straw as support/substrate material. The production of the enzymes lignin peroxidase (LiP), managanese peroxidase (MnP) and cellobiose dehydrogenase (CDH) was followed. The usefulness of the process was tested by assessing the degradation of the herbicides bentazon (3-isopropyl-1H-2,1,3 benzothiadiazin-4(3H)-one 2,3-dioxide) and MCPA (4-chloro-2-methylphenoxyacetic acid). The potential of pure MnP, LiP and CDH to degrade bentazon was examined in vitro. A suitable method for the detection of MnP activity was developed. The detection of LiP activity in fungal straw extracts required appropriate concentrations of veratryl alcohol and hydrogen peroxide and a restricted sample volume. The effect of nitrogen and the hydraulic retention time on enzyme production and bentazon degradation was studied in the laboratory using autoclaved straw. Bentazon degradation was clearly dependent on low nitrogen conditions and on the presence of MnP, both distinct characteristics of the ligninolytic phase of the fungus. For the scaling up of the process, the effects of different amounts of P. chrysosporium inoculum and pre-treatment of straw with formic acid and hot water (50 deg C) on the establishment of P. chrysosporium on unsterile straw were studied. The establishment of the fungus was satisfactory and the presence of other microorganisms did not suppress its growth and activity. Bentazon and MCPA were degraded by 65 and 75%, respectively, in 20 days in the 1.5 m3-bioreactor. The herbicides included LiP and MnP, indicating that these herbicides were degraded by the two enzymes. Pure MnP (with Mn(II) and H2O2) did not oxidize bentazon. However, in the presence of MnP, Mn(II) and Tween 80, bentazon was oxidized, probably by a lipid peroxidation reaction. Bentazon was oxidized significantly faster by LiP as compared to the MnP-Tween 80 system. The role of LiP in SSF remains unclear since LiP activity was inhibited/masked by phenols and extractives present in the straw.